A light-emitting diode light source unit described above is employed as a light source for a facsimile machine, a scanner, etc. This unit has undergone various geometrical optics improvements for obtaining higher illumination intensity available therefrom. For instance, in the case of a light-emitting diode light source known from the Japanese Patent Application “Kokai” No.: Hei. 5-029665 (see paragraphs 0010–0013 and FIG. 2 thereof in particular), on a circuit board, there are arranged, in the form of an array, a plurality of light-emitting diode (LED) elements spaced apart along the length of the board and white resin portions are formed adjacent opposed ends of the array of the LED elements and a transparent resin portion is formed between the opposed white resin portions. Each LED element is die-bonded to a circuit pattern portion of the board, with a top face of the element being wire-bonded to the pattern portion of the board. For forming the white resin portion, there is prepared a semi-liquid material having a high viscosity and a high solidifying speed by mixing a transparent resin material with a white pigment. The two white resin portions are formed by applying this semi-liquid material to the respective positions adjacent the opposed ends of the LED elements array in the form of convex portions progressively raised along the longitudinal direction of the board (i.e. portions having a semi-oval cross section) and then heating the applied material for its solidification. In this, one of the white resin portions is to cover certain portions of the wire bonding and the entire circuit pattern for their protection. A beam emitted from a lateral face of the LED element is reflected by the white resin portion and this reflected beam is then refracted through an interface between the transparent resin portion and ambient air so as to be focused at a position above the LED element.
Another conventional LED light source unit is known from the Japanese Patent Application “Kokai” No. : Hei. 6-291939 (see paragraphs 0029–0030 and FIG. 3 thereof in particular). In this unit, a circuit board mounting thereof a linear array of LED elements is mounted on a resin mount. A portion of this mount extends to the LED mounting surface of the circuit board, with leading ends thereof reaching opposed ends of the LED array, where there are formed inclined faces flared open in a document scanning direction. This inclined face has a surface with a mirror finish, thus forming a reflecting face for the beam emitted from the LED. This beam reflecting face serves for obtaining higher illumination intensity by reflecting the beam emitted from the lateral or front face of the LED element.
In the case of the former-described patent application publication, the white resin portion acting as a “reflector” is formed by applying the material directly to the printed circuit board. Hence, irregularity tends to occur in the spacing relative to each LED element and/or the shape of the reflecting face and such irregularity may invite irregularity in the illumination intensity of the LED array.
In the case of the latter-described patent application publication, the mount including the reflector is designed to hold and support the entire printed circuit board. Hence, this construction results in disadvantageous enlargement of the entire LED light source unit, which makes its application difficult for an optical system imposing a significant space limitation.